In the best case: Contentment.
(If you are a satisfied freelancer, you can stop reading here:)

This is a very theoretical approach to understand the question behind all this, which is: "Why?".

You know what you do and I guess you are an expert on how you do it, but to level-up you still need to know why you do it.

Back to explain the original question:

A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen.
To adapt this model and work with it in my theoretical approach, I draw a much easier picture of what the fuel-cell does:

Simplified explanation of a fuel-cell

Transferring this to a client - freelancer relationship this seems to make no sense at the first impression, well it will, just move a bit closer to the edge of your seat and read on.

It is not your pricing strategy that makes clients come back, but you´ve already guessed that, am I right?

Actually, what keeps you working and doing what you love in your dream career of being a freelancer is not the jobs that you work through, not the great ideas that you always come up with. And no, it probably isn´t your sense of humour that makes people come back. To confuse you even more, I say it is none of the above and all these things together.

Why are people asking you and not someone else? Why is it that you are picked to do this or that illustration, if others are even less expensive?

Satisfaction is the answer.

Note: The word collaboration includes the word "Labor"

Contentment is the result of any great collaboration. Your humour is probably adding to the contentment of the situation if your client comes through as stressed, they feel good to know you aren´t stressed and that is a relief. Also your great ideas are valuable but they can´t stand alone, sometimes it is better to hold back on a great idea to make the client feel better. Sometimes you need to show some teeth and sometimes you have to apologize, just like in any relationship, no one can tell you when you have to do which. You either learn it or die trying, that´s life.

This isn´t about the "Client-is-king" phrase because that would mean, the client is always right, but that is, essentially, not true.

Balance is important.

Contentment should always be on both ends, exactly like the fuel cell works, if there is too much oxygen it will cause the fuel cell to stop, same happens vice-versa. Now you probably understand why this comparison is so important.

If you do all that with the outcome "Satisfaction" in mind, and I mean satisfaction for all parties involved (client, clients client, yourself and clients boss eventually), it will come back to you.

Promised.